fix(payload-import): align with pre-util-linux toolchain by removing mount/S_ISBLK dependencies and probing only existing block nodes

steps/improve/import_payload.sh

@@ -7,8 +7,34 @@ set -ex
 
 if [ "${PAYLOAD_REQUIRED}" = True ]; then
     mkdir -p /external/distfiles
-    if ! payload-import /external/distfiles; then
-        echo "payload-import failed: no payload image found on block devices." >&2
+    found_payload=0
+
+    if [ -r /proc/partitions ]; then
+        while read -r major minor blocks name; do
+            case "${name}" in
+                ""|name|ram*|loop*|fd*|sr*|md*|dm-*|nbd*)
+                    continue
+                    ;;
+                *[0-9])
+                    continue
+                    ;;
+            esac
+            dev_path="/dev/${name}"
+            [ -b "${dev_path}" ] || mknod -m 600 "${dev_path}" b "${major}" "${minor}" >/dev/null 2>&1 || :
+        done < /proc/partitions
+    fi
+
+    for dev_path in /dev/*; do
+        [ -b "${dev_path}" ] || continue
+        if payload-import --probe "${dev_path}"; then
+            payload-import --device "${dev_path}" /external/distfiles
+            found_payload=1
+            break
+        fi
+    done
+
+    if [ "${found_payload}" != 1 ]; then
+        echo "payload-import failed: no payload image found on block devices under /dev." >&2
         exit 1
     fi
 fi